System and method for separating solids from fluids

ABSTRACT

A system for separating solids from fluid including a solid-laden fluid including a base fluid, a first separator configured to receive the solid-laden fluid and separate the fluid into a solids portion and an effluent, and a membrane separator configured to receive the effluent and separate the effluent into a permeate and a concentrate is disclosed. A method for separating solids from fluid including obtaining a solid-laden fluid, wherein the solid-laden fluid comprises a base fluid, feeding the solid-laden fluid through a centrifuge, removing at least a portion of high gravity solids from the solid-laden fluids, flowing the solid-laden fluid through a membrane separator, removing at least a portion of low gravity solids from the solid-laden fluid, and collecting a permeate from the membrane separator is also disclosed.

BACKGROUND OF INVENTION

1. Field of the Invention

Embodiments disclosed here generally relate to a system for separatingsolids from oil-based, synthetic-based, and water-based fluids. Morespecifically, embodiments disclosed herein relate to a system forseparating solids from fluids using a membrane separator.

2. Background Art

When drilling or completing wells in earth formations, various fluidsare used in the well for a variety of reasons. Common uses for wellfluids include: lubrication and cooling of drill bit cutting surfaceswhile drilling generally or drilling-in (i.e., drilling in a targetedpetroliferous formation), transportation of “cuttings” (pieces offormation dislodged by the cutting action of the teeth on a drill bit)to the surface, controlling formation fluid pressure to preventblowouts, maintaining well stability, suspending solids in the well,minimizing fluid loss into and stabilizing the formation through whichthe well is being drilled, fracturing the formation in the vicinity ofthe well, displacing the fluid within the well with another fluid,cleaning the well, testing the well, transmitting hydraulic horsepowerto the drill bit, placing a packer, abandoning the well or preparing thewell for abandonment, and otherwise treating the well or the formation.

Fluids or muds typically include a base fluid and weighting agents tohelp remove cuttings and other solids from the well. During drilling andwellbore treatments, the fluid is usually injected through the center ofthe drill string to the bit and exits through the annulus between thedrill string and the wellbore. During this process, the fluid may cooland lubricate the bit and/or transport drill cuttings and other solidsto the surface. At the surface, a portion of the drill cuttings can beseparated from the fluid and the fluid can be circulated back into thewell for reuse.

Drill cuttings can originate from different geological strata, includingclay, rock, limestone, sand, shale, underground salt mines, brine, watertables, and other formations while other solids may include metal shardsfrom tools and downhole equipment. These solids can range in size fromless than two microns to several hundred microns. Drill cuttings arecommonly classified according to size: smaller than 2 microns areclassified as clay; from 2 to 74 microns, silt; 74 to 500 microns, sand;and larger than 500 microns, cuttings. Several types of separationdevices have been developed to efficiently separate the varied sizes ofthe weighting materials, drill cuttings, and solids from the drillingfluid, including shakers (shale, rig, screen), screen separators,centrifuges, hydrocyclones, desilters, desanders, mud cleaners, mudconditioners, dryers, filtration units, settling beds, sand traps, andthe like.

A typical process used for the separation of drill cuttings and othersolids from fluid includes multiple steps which separate solids fromfluids according to the size of the solids. Fluid returned from a welland containing drill cuttings, additives, and other solids can be fed toa shale shaker. The shale shaker may separate the fluid into largeparticles, such as drill cuttings, and effluent. The fluid and remainingparticles within the effluent can then be passed through a degasser, adesander to remove sand, a desilter to remove silt, and a centrifuge toremove smaller particles. The solids, including any weighting materials,are then discarded and the resulting clean fluid can be reused. In somecases, solids may pass through the degasser, desander, desilter, andcentrifuge, thus ending up with the clean fluid.

In some separating systems, the clean fluid can retain a portion ofsolids which can be recycled downhole with the clean fluid. In somecases the solids can damage the formation and/or downhole equipment.Additionally, small solids can accumulate in the downhole fluid whichmay also be detrimental to the formation. Further, if the solids contentincreases, additional drilling or completions fluid (water, oil, etc.)must be added to dilute the fluid and to maintain the desired weight ofthe fluid. The dilution of the fluid containing solids is often costlyand can alter the balance of chemical and fluid proportions.

Separating systems having separating devices such as, for example,shakers, screen separators, centrifuges, and hydrocyclones, may also beused to separate solids from drilling fluids that are commonly used totreat and maintain welibores. Some separating systems may allow aportion of solid particles to pass through the separating devices alongwith the desired clean fluid, and the solids can also be recycled intothe wellbore with the clean fluid. As described above, solid particlesmay damage formation and/or downhole equipment.

Accordingly, there exists a need for a system and method for effectivelyseparating solids from fluids to obtain a fluid having low solidscontent.

SUMMARY OF INVENTION

In one aspect, the embodiments disclosed herein relate to a system forseparating solids from fluid, the system including a solid-laden fluidincluding a base fluid, a first separator configured to receive thesolid-laden fluid and separate the fluid into a solids portion and aneffluent, and a membrane separator configured to receive the effluentand separate the effluent into a permeate and a concentrate.

In another aspect, the embodiments disclosed herein relate to a methodfor separating solids from fluid, the method including obtaining asolid-laden fluid, wherein the solid-laden fluid includes a base fluid,feeding the solid-laden fluid through a centrifuge, removing at least aportion of high gravity solids, flowing the solid-laden fluid through amembrane separator, removing at least a portion of low gravity solids,and collecting a permeate from the membrane separator.

In yet another aspect, the embodiments disclosed herein relate to amethod of using a membrane separator in an active drilling system, themethod including collecting a used drilling fluid, feeding the useddrilling fluid through a membrane separator, and flowing a permeate intoan active drilling system.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic representation of a separating system inaccordance with embodiments disclosed herein.

FIGS. 1B and 1C are test results of a separating system in accordancewith embodiments disclosed herein.

FIG. 2 is a schematic representation of a separating system inaccordance with embodiments disclosed herein.

FIG. 3 is a schematic representation of a separating system inaccordance with embodiments disclosed herein.

FIG. 4 is a perspective view of a membrane separator in accordance withembodiments disclosed herein.

FIG. 5A is a schematic view of a separating system in accordance withembodiments disclosed herein.

FIGS. 5B, 5C, and 5D are test results of a separating system inaccordance with embodiments disclosed herein.

FIG. 6 is a schematic view of a separating system in accordance withembodiments disclosed herein.

FIG. 7 is a schematic view of a separating system in accordance withembodiments disclosed herein.

FIG. 8 is a schematic view of a separating system in accordance withembodiments disclosed herein.

FIG. 9 is a schematic view of a separating system in accordance withembodiments disclosed herein.

FIG. 10 is a schematic view of a separating system in accordance withembodiments disclosed herein.

FIG. 11 is a schematic view of a separating system in accordance withembodiments disclosed herein.

FIG. 12 is a particle size distribution of a feed fluid in accordancewith embodiments disclosed herein.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein relate to a system andmethod for separating solids from fluids. More specifically, embodimentsdisclosed herein relate to a system and method for separating solidsfrom fluids using a membrane separator.

As described above, a conventional separating system for removing solidsfrom liquids may include devices such as, for example, shakers, screenseparators, centrifuges, and hydrocyclones. In the embodiments disclosedherein, at least one membrane separator is used in a separating system.Additionally, the separating system may include one or more of thedevices listed above. Further, the separating system having a membraneseparator may also include an optional recycle loop and/or means forinjecting separated fluid into an active fluid system, which will bedescribed in detail below.

Referring to FIG. 1A, an exemplary separating system 100 is shown.Solid-laden fluid may be introduced into separating system 100 wheresolid particles may be separated from the fluid. As referred to herein,a solid-laden fluid may contain solid particles in addition to a fluid.The fluid present in the solid-laden fluid may include a base fluidhaving an oil-base, a water-base, and/or a synthetic-base. The solidparticles in the solid-laden fluid may be categorized as gravel, sand,silt, or colloidal solids, according to size. Gravel may include solidsgreater than 2000 microns in size, sand may include solids ranging insize from approximately 74 to approximately 2000 microns, silt mayinclude solids ranging in size from approximately 2 to approximately 74microns, and colloidal solids may be less than approximately 2 micronsin size. While larger solids such as, for example, intermediate solids(greater than approximately 250 microns), medium solids (betweenapproximately 74 to 250 microns), fine solids (between approximately 44to 74 microns), and ultrafine solids (between approximately 2 to 44microns), may be removed by shale shakers, hydrocyclones, settling pits,desanders, and centrifuges, smaller particles, such as colloidal solids,may form colloidal suspensions in the fluid and may continue tocirculate through the system. As such, the concentration of colloidalsolids may continue to build up in the fluid until the concentration hasan adverse effect on fluid properties and stability.

In certain drilling fluids, weighting materials such as, for example,barite or bentonite may be used to adjust drilling fluid properties.While the weighting material may be introduced into the drilling fluidas a high gravity solid (HGS) having a specific gravity greater thanapproximately 4.2 and a size greater than approximately 2 microns,multiple circulations of the weighting material during drilling maypulverize the weighting material particles. Typical solids removalequipment may not be able to remove the colloidal particles, andcolloidal material including pulverized weighting material may build upwithin the drilling fluid.

A number of variable parameters may effect the operation of separatingsystem 100. Parameters such as, for example, viscosity, temperature,pressure, and volumetric flow rate may impact the flux, i.e., the amountof fluid that flows through a unit area per unit time, of separatingsystem 100. In certain embodiments, the temperature of feed fluid 102may be between approximately 70 and 200 degrees Fahrenheit.Additionally, the pressure of fluid within separating system 100 may bebetween approximately 10 and 150 psi. Further, the volumetric flow rateof fluid within separating system 200 may be between approximately 5 and50 gpm. Adjustments to parameters such as, for example, viscosity,temperature, pressure, and volumetric flow rate may increase the flux ofseparating system 100.

As disclosed above, feed fluid 102 may include high gravity solidsand/or low gravity solids. First separator 104, i.e. centrifuge, hydrocyclone, VERTI-G™, or the like, separates feed fluid 102 into acentrifuge underflow 106 and a centrifuge overflow 108. Centrifugeunderflow 106 may contain a substantial portion of high gravity solidsthat may have been present in feed fluid 102. Centrifuge underflow 106may be collected and removed from or recycled through separating system100. Centrifuge overflow 108 may contain a relatively small amount ofhigh gravity solids, but may still contain a substantial amount of lowgravity solids that may have been present in feed fluid 102. Centrifugeoverflow 108, which may still be defined as a solid-laden fluid due tothe presence of low gravity solids and/or high gravity solids therein,then flows to membrane separator 110 for further separation.

Membrane separator 110 may separate centrifuge overflow 108 into aconcentrate 114 and a permeate 112. Concentrate 114 may include asubstantial amount of low gravity solids and/or high gravity solids thatmay have been present in centrifuge overflow 108. Permeate 112 includesthe filtered fluid that passes through membrane separator 110. Incertain embodiments, permeate 112 may contain a total solids content ofapproximately 0.5% by volume.

Referring to FIG. 2, a separating system 200 is shown having eachelement as described above with respect to FIG. 1A. Separating system200 may further include an optional recycle loop 116A through whichconcentrate 114 may flow, such that concentrate 114 is introduced toseparating system 200 after first separator 104 and before membraneseparator 110. Alternatively, separating system 200 may include recycleloop 116B which introduces concentrate 114 into separating system 200before first separator 104. In certain embodiments, either or both ofrecycle loops 116A and 116B may be used. In such an embodiment,concentrate 114 may pass through membrane separator 110 multiple times.Each cycle of recycled fluid through membrane separator 110 may resultin concentrate 114 having a greater solids content. An increase inconcentrate 114 solids content may also increase the viscosity ofconcentrate 114. With an increase in viscosity, additional energy may berequired to pump concentrate 114 through membrane separator 110 andrecycle loop 116. Accordingly, in certain embodiments, concentrate 114may pass through recycle loop 116 a number of times before reaching acritical viscosity and, once reached, concentrate 114 may be removedfrom separating system 200. The critical viscosity may be chosen basedon pumping capacity, system efficiency, or other parameters.Alternatively, rather than removing the fluid at critical viscosity, thetemperature of the fluid may be increased and/or viscosity reducers maybe added such that the viscosity of the fluid flowing through separatingsystem 200 may be decreased.

In another embodiment, a heat exchanger (not shown) may be included inseparating system 200 to increase the temperature of concentrate 114,thereby decreasing the viscosity of concentrate 114. Decreasing theviscosity of concentrate 114 may allow easier pumping of concentrate 114through membrane separator 110 without increasing pumping pressure.Accordingly, in select embodiments, a concentrate in a separating systemwith a heat exchanger may make a greater number of passes throughmembrane separator 110 before reaching a critical viscosity than aconcentrate 114 in a separating system without a heat exchanger.Additionally, economic benefits may be achieved due to increased pumpingefficiency.

Referring to FIG. 3, a separating system 300 is shown having eachelement as described above with respect to FIG. 1A. Separating system300 further shows a slip stream 109, a wellbore 118, and an active mudsystem 120 that may be fluidly connected with a drill string and a drillbit of a drilling system, as previously described. Feed fluid 102 may bea solid-laden fluid including water-based, oil-based, and/orsynthetic-based fluids that may be obtained from wellbore 118.

In certain embodiments, separating system 300 may operate continuously.For example, a solid-laden fluid may be obtained from wellbore 118. Thesolid-laden fluid, i.e., feed fluid 102, may be fed into separatingsystem 300 wherein solids and fluids contained in the solid-laden fluidare separated using centrifuge 104. Centrifuge overflow 108 may thenflow through slip stream 109 to active mud system 120 or may passthrough membrane separator 110 in accordance with embodiments disclosedabove. Permeate 112 may be obtained from membrane separator 110 and maybe injected into active mud system 120. In certain embodiments,additives 122 may also be added to active mud system 120. Additives 122may include new drilling fluids, thinners, weighting agents, losscontrol materials, and/or conditioners that may alter the composition orcharacteristics of drilling fluids. The reconstituted drilling fluid maythen be injected into wellbore 118 as shown by arrow 124.

Referring to FIG. 4, an example of a membrane separator 110 inaccordance with embodiments disclosed herein is shown. In thisembodiment, membrane separator 110 is tube shaped and may be made ofstainless steel. In certain embodiments, membrane separator 110 may bemade of type 316L stainless steel sintered with titanium dioxide (TiO₂).Alternatively, Hastelloy® C, high nickel alloy, or ceramic membranes maybe used. For example, ceramic membranes, commercially available fromCoMeTas of Copenhagen, Denmark, made partially or entirely from siliciumcarbide (SiC) may be used.

One of ordinary skill in the art will appreciate that dimensions ofmembrane separator 110, such as, for example, length 402, diameter 404,and thickness 406, may affect the amount of permeate 112 collected perunit volume of centrifuge overflow passed through membrane separator110. Additionally, dimensions such as length 402, diameter 404, andthickness 406 may be adjusted based on the composition of thesolid-laden fluid being passed through membrane separator 110 and/or thedesired amount or composition of permeate 112. In certain embodiments,membrane separator 110 may have an inside diameter in a range ofapproximately 0.25 and 1 inches, and a thickness in a range ofapproximately 50 and 100 micron.

Pores 408 may be disposed in membrane separator 110 such that fluid maymove from the inside to the outside of membrane separator 110. Pores 408may have a specific pore size, thereby controlling the type and amountof fluid that may flow from inside membrane separator 110 to theoutside. Pore size may also be chosen to prevent substantially smallsolid particles from entering and clogging pores 408. In certainembodiments, the pore size of pores 408 may be between 0.02 and 0.5micron for TiO2 sintered 316L stainless steel or 0.02 to 2 micron forceramics. Pore size may be chosen based on the concentrations and sizesof particles present within the fluid. For example, a pore size may beselected to be slightly smaller than the smallest particles present inthe fluid so that particles from the fluid do not become lodged in pores408, thereby plugging membrane separator 110. Additionally, a largerpore size may allow an increased amount of oil to pass through pores 408and may increase the amount of oil flux through membrane separator 110.

Membrane separator 110 may further include a first opening 410 and asecond opening 412 through which fluid may flow. In certain embodiments,membrane separator 110 may have an inner surface 416 and an outersurface 414 disposed between first and second openings 410, 412, suchthat cross-flow filtration through pores 408 may occur. One of ordinaryskill in the art will appreciate that cross-flow filtration occurs whena solid-laden fluid flows in a first direction parallel to a filter andwhen a portion of the solid-laden fluid passes through the filter in asecond direction that is approximately perpendicular to the firstdirection.

Referring to FIGS. 1A and 4 together, a flow pattern for a solid-ladenfluid passing through membrane separator 110 is described. A solid-ladenfluid, specifically, centrifuge overflow fluid 108, may flow intomembrane separator 110 through first opening 410. Centrifuge overflowfluid 108 may contact inner surface 416 as it passes through membraneseparator 110 toward second opening 412 in a first direction parallel toa central axis 418 of membrane separator 110. A portion of centrifugeoverflow fluid 108 may pass through pores 408 to outer surface 414 in adirection approximately perpendicular to the first direction of flow ofcentrifuge overflow fluid 108, as indicated by arrow A. The fluidpassing from inner surface 416 through pores 418 to outer surface 414 isdefined herein as permeate 112.

Those of ordinary skill in the art will appreciate that more than onemembrane separator 110, disposed in series or in parallel, may be usedin a single separating system. Additionally, membrane separator 110 mayhave various membrane separator lengths, membrane separator diameters,and/or membrane separator thicknesses. Further, membrane separator 110may include pores of various pore sizes.

Referring now to FIG. 7, an example of a separating system usingchemical additives is shown. Separating system 700 includes mud, i.e., asolid-laden fluid, from a mud source 702. Mud source 702 may be, forexample, a mud storage container or an active mud system. Chemicaladditives from a first chemical source 704 may be added to the mud,creating a first mixture. In certain embodiments, the chemicalsadditives may include anionic surfactants, nonionic surfactants, alkylpolyglycosides, and combinations thereof. Other chemical additives thatmay also be used include, for example, EMR-953 and EMR-961 availablefrom M-I Swaco L.L.C., Houston, Tex. The first mixture may then bepumped through a pump 706, as shown. Additional chemical additives froma second chemical source 708 may then be added to the first mixture tocreate a second mixture. The second mixture may then be pumped through amixing system 710 which may include, for example, an agitator or aneductor. The second mixture may be pumped from mixing system 710 to acentrifuge 712 where a portion of solids may be removed from the secondmixture and may be collected or discarded at 714. Additives 724 may beadded to the remaining portion of the second mixture. In certainembodiments, additives 724 may include viscosity reducers and/ordemulsifiers. A remaining portion of the second mixture may then bepumped through a membrane separator 716 in accordance with embodimentsdisclosed herein. A permeate fluid 718, having a low solids content, maybe collected for recycling into the active mud system. A concentratefluid 720, having a relatively high solids content, may be collected forrecycling, e.g., disposal, reprocessing, etc. In certain embodiments,concentrate fluid 720 may pass through an optional recycle loop 722,wherein concentrate fluid 720 is re-injected into separating system 700.One of ordinary skill in the art will appreciate that concentrate fluid720 may be injected at any step in separating system 700. For example,concentrate fluid 720 may be introduced into separating system 700 atconcentrate injection points A, B, C, or D. In select embodiments,permeate fluid 718 may be directly injected into an active mud system,or may be mixed with new mud or additives before being injected into anactive mud system. In other embodiments, permeate fluid 718 may becollected for later use.

Those of ordinary skill in the art will appreciate that first chemicalsource 704 and second chemical source 708 may include, for example,surfactants or flocculants. Accordingly, a surfactant may be injectedinto separating system 700 before a flocculant, or a flocculant may beinjected before a surfactant. In certain embodiments, chemical additivescontained in first and second chemical sources 704, 708 may include, forexample, chemicals from the polyhydroxyl fatty acid family. For example,Surethin®, Novathin™, Rheduce®, and Versathin®, available from M-I SwacoL.L.C., Houston, Tex. may be added prior to feeding the material tomembrane separator 716. Additionally, acid such as hydrochloric acid(HCl), may also be added. Further, one of ordinary skill in the art willappreciate that more or less than one centrifuge may be used inseparating system 700, and that more than one membrane separator mayalso be used.

After a separating system in accordance with embodiments disclosedherein is used, it may be cleaned using a variety of cleaning fluidssuch as, for example, recovered oil, soap solution, nitric acid, asolvent, surfactants, or base oil.

EXAMPLES

Several tests were conducted to obtain data regarding the separationcapabilities of a system having two centrifuges and the separationcapabilities of a system having one centrifuge and one membraneseparator. The tests and results are described below:

Example 1 Multiple Centrifuge System

The test described in this example was conducted to obtain dataregarding the separation capabilities of a system having twocentrifuges. Referring to FIG. 5A, a feed fluid 502 was introduced intoa first centrifuge 504. The first centrifuge had a 14″ diameter, a 34″stainless steel bowl and conveyor assembly, and a 25 hp motor. Afterseparation in first centrifuge 504, a first centrifuge underflow 506 wasremoved from separating system 500. A first centrifuge overflow 508 wasthen transferred from first centrifuge 504 to a second centrifuge 510.Second centrifuge 510 was 14″ in diameter, had a 57.5″ stainless steelbowl and conveyor assembly, and a 25 hp motor. After separation insecond centrifuge 510, a second centrifuge underflow 512 was removedfrom system 500. Finally, a second centrifuge overflow 514 was obtainedfrom second centrifuge 510. The properties and compositions of feedfluid 502, first centrifuge underflow 506, first centrifuge overflow508, second centrifuge underflow 512, and second centrifuge overflow514, after one cycle through separating system 500 are illustrated inTable 1, below:

TABLE 1 Results of Filtration of Oil-Based Muds using Centrifuges FirstSecond Second Centrifuge Centrifuge Centrifuge Feed Fluid OverflowUnderflow Overflow Specific Gravity 1.65 1.25 — 1.06 Oil Content (% byvol) 53.5 59 11.3 64 Water Content (% by vol) 21.5 26 6 26 SolidsContent (% by vol) 25 15 82.7 10 High Gravity Solids Con- 17.98 9 — 4.09tent (% by vol) Low Gravity Solids Con- 6.07 5 — 4.24 tent (% by vol)

Table 1 shows that as feed fluid 502 passed through separating system500, solids were removed from liquid. In this particular test, feedfluid 502 had a solids content of 25%, an oil content of 53.5%, a watercontent of 21.5%, and a specific gravity of 1.65. Specifically, highgravity solids made up 17.98% and low gravity solids made up 6.07% offeed fluid 502. After passing through first centrifuge 504, the solidscontent of first centrifuge overflow 508 was approximately 15%, highgravity solids accounting for 9% and low gravity solids accounting for5%, oil content was 59%, and water content was 26%. Accordingly, thespecific gravity of first centrifuge overflow 508 decreased to 1.25.

Second centrifuge underflow 512 exited second centrifuge 510 having asolids content of 82%, an oil content of 11.3%, and a water content of6%. Second centrifuge overflow 514 exited second centrifuge 510 having asolids content of 10%, with high gravity solids accounting for 4.09% andlow gravity solids accounting for 4.24%. Additionally, second centrifugeoverflow 514 had an oil content of 64%, a water content of 26%, and aspecific gravity of 1.06. Thus, second centrifuge overflow fluid 514 maybe obtained from feed fluid 502 by passing feed fluid 502 throughseparating system 500, and may have decreased specific gravity,increased percent volume of oil and water, decreased percent volume ofhigh gravity solids, and decreased percent volume of low gravity solids.

Referring now to FIGS. 5B and 5C, particle size distribution (PSD)graphs are shown for first centrifuge overflow 508, and secondcentrifuge overflow 514, respectively. According to FIG. 5B, the d50particle size for first centrifuge overflow 508 was 8.187 micron.Referring to FIG. 5C, the d50 particle size for second centrifugeoverflow 514 was 4.796 micron. Thus, second centrifuge 510 was able toremove a portion of the larger particles present in first centrifugeoverflow 508, resulting in a decrease of the d50 particle size.

In some cases, chemicals may be added to feed fluid 502 or firstcentrifuge overflow 508 to further reduce the d50 of second centrifugeoverflow 514. Chemicals that may be added include, for example, anionicsurfactants, nonionic surfactants, alkyl polyglycosides, andcombinations thereof. Referring to FIG. 5D, a PSD graph of a secondcentrifuge overflow fluid from a separating system using chemicaladditives is shown. The PSD shows that, in this example, a secondcentrifuge overflow from a separating system using chemical additiveshad a d50 of 1.082 micron.

Example 2 Centrifuge and Membrane Separator System

In a second test, the separation capability of a system including acentrifuge disposed in series with a membrane separator was analyzed.Referring back to FIG. 1A, a feed fluid 102 was introduced into acentrifuge 104. Centrifuge 104 had a 14″ diameter, a 34″ stainless steelbowl and conveyor assembly, and a 25 hp motor, but one of ordinary skillin the art will appreciate that other centrifuges may be used. Afterseparation in centrifuge 104, a centrifuge underflow 106 was removedfrom separating system 100. A centrifuge overflow 108 then flowed fromcentrifuge 102 to membrane separator 110. In this test, a 0.1 micronmembrane separator was used; however, any membrane separator inaccordance with embodiments disclosed herein may be used. A permeate 112filtered through membrane separator 110 while a concentrate 114 wasremoved from separating system 100. The properties and compositions offeed fluid 102, centrifuge underflow 106, centrifuge overflow 108,concentrate 114, and permeate 112 are provided in Table 2, below.

TABLE 2 Results of Filtration of Oil-Based Muds using a Centrifuge and aMembrane Separator Membrane Membrane Centri- Separator Separator VirginFeed fuge Concen- Perme- Base Fluid Overflow trate ate Oil Specific 1.561.3 1.38 0.79 0.79 gravity Oil Content 50.5 54 49.5 98.5 100 (% by vol)Water 24.5 27 31.5 0 — Content (% by vol) Solids 25 19 19 1.5 — Content(% by vol) High Gravity 15.11 5.67 Not Not detected — Solids measuredContent (% by vol) Low Gravity 8.64 11.97 Not Not detected — Solidsmeasured Content (% by vol) Electrical 263 283 230 >1999 — Stability (V)Plastic 39 23 Not Not — Viscosity measured measured (cP)Turbidity >100 >100 Not 2.2 — (NTU) measured

Table 2 shows that as feed fluid 102 passed through separating system100, solids were removed from liquid and were concentrated in centrifugeunderflow 106 and in concentrate 114. In this test, feed fluid 102 hadan initial solids content of 25% with high gravity solids accounting for15.11% and low gravity solids accounting for 8.64%. After passingthrough centrifuge 104, the solids content of centrifuge overflow 108was 19% with high gravity solids making up 5.67% and low gravity solidsmaking up 11.97%. The solids content of centrifuge underflow fluid 106was 58% and centrifuge underflow 106 was removed from the system.Centrifuge overflow 108 then passed through membrane separator 110.After passing through membrane separator 110, the solids content ofpermeate 112 was measured at 1.5% and the solids content of concentrate114 was 19%. The solids content of permeate 112 was an experimentalerror due to return analysis, as the result should have been less than0.5 percent. The percent by volume of low gravity solids and the percentby volume of high gravity solids present in permeate 112 were too low tobe measured and no water content was detected in permeate 112.

Electrical stability, plastic viscosity, and turbidity measurements werealso taken at certain points during the test. Electrical stability offeed fluid 102 was 263 V. After passing through centrifuge 104, theelectrical stability of centrifuge overflow 108 was approximately 283 Vand, after passing through membrane separator 110, the electricalstability of membrane separator permeate 112 was greater than 1999 V.Plastic viscosity of feed fluid 102 was 39 centipoise and the plasticviscosity of centrifuge overflow 108 was 23 centipoise. Additionally,the turbidity measurement of membrane separator permeate 112 was 2.2NTU. Thus, the measurements taken of feed fluid 102, centrifuge overflow108, and membrane separator permeate 112, indicate that solids wereremoved from feed fluid 102 by centrifuge 104 and membrane separator110.

Additional information regarding the solids content of the fluids may befound in FIGS. 1B and 1C which show PSD graphs for centrifuge overflow108 and concentrate 114, respectively. FIG. 1B shows that, in this test,the d50 particle size for centrifuge overflow 108 was 5.49 micron. Theturbidity for centrifuge overflow 108 was 179.3 NTU. FIG. 1C shows that,in this test, the d50 particle size for concentrate 114 was 4.799micron. A PSD graph for permeate 112 could not be generated because novisible particles were present in permeate 112. Thus, membrane separatorpermeate 112, obtained from feed fluid 102 by passing feed fluid 102through separating system 100, may have decreased specific gravity,increased percent volume of oil and water, decreased percent volume ofhigh gravity solids, and decreased percent volume of low gravity solidswhen compared with feed fluid 102.

Additionally, Table 3 below shows a comparison of membrane separatorpermeate 112 and second centrifuge overflow fluid 514, from Example 1.

TABLE 3 Second Centrifuge Overflow and Membrane Separator PermeateSecond Centrifuge Membrane Separator Overflow Permeate Specific Gravity1.06 0.79 Oil Content (% by vol) 64 98.5 Water Content (% by vol) 26 0Solids Content (% by vol) 10 1.5 High Gravity Solids Content 4.09 — (%by vol) Low Gravity Solids Content 4.24 — (% by vol) ElectricalStability (V) — >1999 Plastic Viscosity (cP) — — Turbidity (NTU) — 2.2

As shown in Table 3, the specific gravity of membrane separator permeate112 is 0.79 which is significantly lower than the specific gravity ofsecond centrifuge overflow 514 which was 1.06. Additionally, the oilcontent of membrane separator permeate 112 is significantly higher thanthat of second centrifuge overflow 514. Specifically, the oil content ofmembrane separator permeate 112 was approximately 64% while the oilcontent of membrane separator permeate 112 was around 98.5%. Further,the solid content of second centrifuge overflow 514 was approximately10%, with 4.09% being high gravity solids and 4.24% being low gravitysolids. Membrane separator permeate 112 had a solid content of around1.5%. As discussed above, permeate 112 solids content of 1.5% is anexperimental error, as the results should have been less than 0.5%.Thus, the percent of solid content of membrane separator permeate 112was significantly less than the percent of solid content of secondcentrifuge overflow fluid 514.

Example 3 Membrane Separator Filtration of a Used Drilling Fluid

In this test, solid-laden fluid 604 included a synthetic IO 1618-baseddrilling fluid, specifically, Rheliant® System drilling fluid. Referringto FIG. 6, solid-laden fluid 604 was introduced to a feed tank 602 inseparating system 600. From feed tank 602, solid-laden fluid 604 passedthrough valve 606 to feed pump 608. In this test, membrane module 616included six membrane separators (not independently illustrated)connected in series with welded u-bends and enclosed by a permeatecollection shell. Additionally, the membrane separators were made ofsintered 316L stainless steel having a coating of sintered titaniumdioxide and a pore size of 0.1 micron. The total membrane separator areafor this test was 0.754 square feet.

As shown in separating system 600, a pressure gauge 618 measured thepressure of solid-laden fluid 604 entering membrane module 616 andmeasured the pressure of concentrate 620 exiting membrane module 616.Concentrate 620 then flowed past a series of valves, through heatexchanger 622, and back into feed tank 602. In this test, cooling waterwas passed through heat exchanger 622 to decrease the temperature ofconcentrate 620 rather than to increase it. However, due to pump work,the temperature of concentrate 620 still increased slightly despite thecooling effect of heat exchanger 622. In this test, feed tank 602required manual agitation due to the high viscosity of solid-laden fluid604, and the test was terminated after collecting a sample of permeate624.

Example 4 Addition of Demulsifiers to Membrane Separator Feed Fluid

Referring to FIG. 8, a separating system 800 is shown havingdemulsifiers 802 that may be added to feed fluid 804 before feed fluid804 enters membrane separator 806. Membrane separator 806 may divide thefeed fluid and demulsifier mixture into a concentrate 808 and a permeate810. Permeate 810 may pass through an oil/water separator 812 whichseparates permeate 810 into oil 814 and water 816.

To simulate the effects of demulsifiers on a system similar toseparating system 800 during experimentation, demulsifiers were added tomud samples at varying temperatures. The mixtures were stirred,transferred to 50 mL centrifuge tubes, and transferred to a centrifugefor ten minutes. Properties of a feed fluid sample prior to the additionof demulsifiers are included in Table 4 below.

TABLE 4 Properties of Centrifuge Effluent Prior to Addition ofDemulsifiers Temper- Oil Oil Water Water Solids Solids ature (% by vol)(mL) (% by vol) (mL) (% by vol) (mL) 950° F. 62.5 31.25 29 14.5 8.5 4.25

In this test, two demulsifiers, EMR-961 and EMR-953, were used atconcentrations of 1% by volume and 2% by volume. The demulsifiers wereadded to a mud sample and the mixture was stirred. The mixture was thentransferred to a 50 mL centrifuge tube and was subjected tocentrifugation for approximately ten minutes. The tests were conductedat 68 degrees Fahrenheit and at 160 degrees Fahrenheit. The resultingphases were recorded by performing a retort analysis at 950 degreesFahrenheit and the results of the retort analysis can be found in Tables5 and 6 below.

TABLE 5 Filtration using Demulsifiers added to Centrifuge Effluent at68° F. Electrical Sample Volume Water Concentration Stability (Liquidsample + Oil Emulsion Water Solids Separated Demulsifier (% by vol)(Volts) Demulsifier) (mL) (mL) (mL) (mL) (mL) (%) EMR-961 1% 134.33 50 530 12 3 83 EMR-961 2% 96.33 50 9 28 10 3 69 EMR-953 1% 119.00 50 7 30.59.5 3 66 EMR-953 2% 121.33 50 9 26 12 3 83

TABLE 6 Filtration using Demulsifiers added to Centrifuge Effluent at160° F. Electrical Sample Volume Water Concentration Stability (Liquidsample + Oil Emulsion Water Solids Separated Demulsifier (% by vol)(Volts) Demulsifier) (mL) (mL) (mL) (mL) (mL) (%) EMR-961 1% 421.33 50 928 9 4 62 EMR-961 2% 215 47.5 10 25 8.5 4 62 EMR-953 1% 99.33 47.5 7.530 7 3 51 EMR-953 2% 177 47.5 7.5 26 10 4 73

The test results in Tables 5 and 6 show that when added to centrifugeeffluent, EMR-961 at 1% by volume gave 83% water recovery at 68° F. and62% water recovery at 160° F. At 2% by volume, EMR-961 gave 69% waterrecovery at 68° F. and 62% water recovery at 160° F. Demulsifier EMR-953at 1% by volume gave 66% water recovery at 68° F. and 51% water recoveryat 160° F. EMR-953 at 2% by volume gave 83% water recovery at 68° F. and73% water recovery at 160° F. Thus, the addition of demulsifiers to aslurry may break emulsions within the slurry, thereby assisting inseparating water content from the slurry.

Example 5 Addition of Demulsifiers to a First Membrane Concentrate

Referring to FIGS. 9 and 10, separating systems 900 and 1000 are shownhaving a feed fluid 902 in fluid communication with a first membraneseparator 904. First membrane separator 904 divides feed fluid 902 intofirst permeate 908 and first concentrate 910. In separating system 900,demulsifiers 912 are added to first concentrate 910 and the mixture isdirected to a second membrane separator 914. Second membrane separator914 divides the mixture of demulsifiers 912 and first concentrate 910into a second concentrate 916 having a high solids content and a secondpermeate 918 having a high water content. Second permeate 918 is fed toan oil/water separator 920 where it is separated into oil 922 and water924. Referring specifically to FIG. 10, in separating system 1000,demulsifiers 912 are added to first concentrate 910 and the mixture isdirected to a centrifuge 1014. Centrifuge 1014 separates the mixture ofdemulsifiers 912 and first concentrate 910 into an under flow 1016having a high solids content, and an overflow 1018 having oil, water,and a low solids content.

To simulate the effects of demulsifiers on a system similar toseparating system 900, demulsifiers were added to mud samples at varyingtemperatures. Properties of a concentrate sample prior to the additionof demulsifiers are included in Table 7 below. The mixtures werestirred, transferred to 50 mL centrifuge tubes, and transferred to acentrifuge for ten minutes.

TABLE 7 Properties of Membrane Concentrate Prior to Addition ofDemulsifiers Temper- Oil Oil Water Water Solids Solids ature (% by vol)(mL) (% by vol) (mL) (% by vol) (mL) 950° F. 39.5 19.75 49.5 24.8 115.45

In this test, two demulsifiers, EMR-961 and EMR-953, were used atconcentrations of 1% by volume and 2% by volume. Each of the tests wasconducted at 68 degrees Fahrenheit and at 160 degrees Fahrenheit. Theresulting phases were recorded and can be found in Tables 8 and 9 below.

TABLE 8 Filtration using Demulsifiers added to Membrane SeparatorEffluent at 68° F. Electrical Sample Volume Stability (Liquid sample +Oil Emulsion Water Solids Water Demulsifier (Volts) Demulsifier) (mL)(mL) (mL) (mL) (mL) Separated (%) EMR-961 3.67 50 0 24.5 21.5 4 87EMR-961 2.33 50 0 22.5 23.5 4 95 EMR-953 7.33 50 0 50 0 0 0 EMR-953 3.3350 0 25 20 5 81

TABLE 9 Filtration using Demulsifiers added to Membrane SeparatorEffluent at 160° F. Electrical Sample Volume Stability (Liquid sample +Oil Emulsion Water Solids Water Demulsifier (Volts) Demulsifier) (mL)(mL) (mL) (mL) (mL) Separated (%) EMR-961 68 39 0 16.5 18.5 4 96 EMR-96118.67 40 0 17.5 18.5 4 93 EMR-953 56.67 42.5 0 35 3.5 4 17 EMR-953 3.6740 0 20 15 5 76

The test results in Tables 8 and 9 show that, when added to a membraneseparator concentrate, EMR-961 at 1% by volume gave 87% water recoveryat 68° F. and 96% water recovery at 160° F. At 2% by volume, EMR-961gave 95% water recovery at 68° F. and 93% water recovery at 160° F.Demulsifier EMR-953 at 1% by volume gave 0% water recovery at 68° F. and17% water recovery at 160° F. EMR-953 at 2% by volume gave 81% waterrecovery at 68° F. and 76% water recovery at 160° F.

Example 6 Addition of Dispersant to a Synthetic Based Mud

Referring to FIG. 11, a separating system 1100 is shown. Separatingsystem 1100 may include a fluid inlet 1102 configured to receive a feedfluid, and a pump 1104 configured to pump the feed fluid to a series ofmembrane separators 1106, 1108, 1110, 1112. A permeate may be collectedfrom membrane separators 1106, 1108, 1110, 1112 at exits 1114, 1116,1118, 1120, respectively. A concentrate may be pumped through each ofmembrane separators 1106, 1108, 1110, 1112, and may then be mixed intothe feed fluid, thereby recirculating the concentrate through separatingsystem 1100. In certain embodiments, a heat exchanger 1122 may be usedto increase or decrease the temperature of the concentrate and/or thefeed fluid.

In this test, separating system 1100 included membrane separators 1106,1108, 1110, 1112 selected to provide a total membrane separator area of15 square feet. Additionally, Rheliant System® drilling fluid including2 pounds per barrel (“ppb”) of Rheduce® dispersant was selected as thefeed fluid. A PSD of the feed fluid is shown in FIG. 12. Properties ofthe feed fluid, permeate, and concentrate are shown below in Table 10.

TABLE 10 Properties of Rheliant System ® with Rheduce ® Feed Fluid,Permeate, and Concentrate Oil Water Solids Chloride Density (% by (% by(% by content Electron (ppg) wt.) wt.) wt.) (mg/l) Stability Feed Fluid8.68 50.13 26.61 23.26 35000 — Permeate 6.61 — — — — >1999 Concentrate10.83 39.14 13.68 47.18 87000 —

The feed fluid having a density of 8.68 ppg was circulated throughsystem 1100 for approximately 4.25 hours. The feed fluid was separatedby separating system 1100 into a permeate having a decreased density of6.61 ppg and a concentrate having an increased density of 10.83 ppg. Ascan be seen from Table 10, the separating system 1100 separated thechloride content into the concentrate and increased the density of thechloride content. Approximately 65% by weight of the oil containedwithin the feed fluid was collected. Because no visual particles werepresent in the permeate, a PSD could not be performed.

Example 7 Membrane Separator Filtration of Versapro® Drilling Fluid

In this test, separating system 1100 was used to separate a sample ofVersapro® drilling fluid, commercially available from Hagemeyer NorthAmerica, Inc. of Charleston, S.C. Initial feed fluid properties inaddition to collected permeate and concentrate properties can be foundbelow in Table 11.

TABLE 11 Properties of Versapro ® Feed Fluid, Permeate, and ConcentrateOil Water Solids Chloride Density (% by (% by (% by content Electron(ppg) wt.) wt.) wt.) (mg/l) Stability Feed Fluid 8.7 57.75 18.02 24.2738500 — Permeate 6.87 — — — — >1999 Concentrate 10.66 43.95  8.03 48.0294000 —

The feed fluid having a density of 8.7 ppg was circulated through system1100 for approximately five hours. The feed fluid was separated byseparating system 1100 into a permeate having a density of 6.87 ppg anda concentrate having a density of 10.66 ppg. As can be seen from Table11, the separating system 1100 separated the chloride content of thefeed fluid into the concentrate, and increased the concentration of thechloride content. Approximately 65% by weight of the oil containedwithin the feed fluid was collected. Because no visual particles werepresent in the permeate, a PSD could not be performed.

A limited number of exemplary embodiments of the present invention havebeen discussed herein. Those having ordinary skill in the art willappreciate that a variety of separating systems may be designed that arewithin the scope of the present disclosure. Depending on a variety offactors such as, for example, slurry composition, space constraints,environmental restrictions, etc., it may be advantageous to adapt acertain separating system disclosed herein to comply with designrequirements. For example, it may be advantageous to include one or morerecycle loops, wherein each recycle loop directs fluid from a desiredpoint in the system to a preceding point in the system. It may also beadvantageous to include at least one heat exchanger, wherein the heatexchanger increases or decreases the temperature of a fluid in thesystem. Further it may be advantageous to inject at least one chemicaladditive into a slurry in at least one point in the system. By alteringseparating systems disclosed herein, unique separating systems may bedesigned to meet specific performance and design requirements.

A separating system in accordance with embodiments disclosed herein mayadvantageously have a small footprint that may be accommodated on anoff-shore drilling rig platform. Additionally, embodiments disclosedherein may provide a robust mechanical separating system that may beused continuously during drilling and other wellbore treatmentoperations. Furthermore, a variety of solid-laden fluids may be treatedusing the mechanical process disclosed above regardless of theformulation or composition thereof.

Separating systems in accordance with embodiments disclosed herein mayalso reduce or eliminate costs associated with building new fluids andtreating spent fluids using chemical additives. Eliminating the need forchemical additives may increase the predictability of success of theseparating system by eliminating the variability associated withchemical-based processes. Further, eliminating the use of chemicaladditives and the building of new fluids may improve health, safety, andenvironmental conditions. Additionally, the risk of carryover oftreatment chemicals which may be detrimental for final product usagesuch as, for example, polymers and surfactants, may be eliminated.

Permeate collected from a separating system in accordance withembodiments disclosed herein may advantageously contain few or nosolids. Specifically, as discussed above in examples 1 and 2, aseparating system having multiple centrifuges may produce a fluid having10% solids content while a separating system including a membraneseparator, in accordance with embodiments disclosed herein, may producea permeate having approximately 0.5% solids content. Thus, a separatingsystem including a membrane separator may significantly reduce theamount of solids present in a filtered fluid. Additionally, in selectembodiments, the present disclosure may provide a separating system thatmay be used to continuously accept solid-laden fluids from a wellbore,separate solids from fluids, and return fluids to the wellbore.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A system for separating solids from fluid, the system comprising: asolid-laden fluid comprising a base fluid; a first separator configuredto receive the solid-laden fluid and separate the fluid into a solidsportion and an effluent; and a membrane separator configured to receivethe effluent and separate the effluent into a permeate and aconcentrate.
 2. The system of claim 1, wherein the membrane separator issubstantially tube shaped, and comprises a plurality of openingsconfigured to allow cross-flow through the tube.
 3. The system of claim2, wherein the permeate passes through a plurality of pores and whereinthe concentrate passes through the plurality of openings.
 4. The systemof claim 1, wherein the membrane separator comprises a stainless steelmembrane surface sintered with titanium dioxide.
 5. The system of claim1, wherein the membrane separator comprises a plurality of pores havinga pore size in a range between 0.02 micron and 0.5 micron.
 6. The systemof claim 1, wherein the system further comprises a heat exchanger. 7.The system of claim 1, wherein the base fluid comprises at least one ofan oil-base, a synthetic-base, and a water-base.
 8. The system of claim1, wherein the solid-laden fluid enters the membrane separator at apressure of approximately 100 psi.
 9. The system of claim 1, wherein thesolid-laden fluid enters the membrane separator at a temperature ofapproximately 190 degrees Fahrenheit.
 10. The system of claim 1, whereinthe solid-laden fluid enters the membrane separator at a flow rate ofbetween approximately 10 and 30 gpm.
 11. The system of claim 1, whereinthe centrifuge is configured to remove high gravity solids and whereinthe membrane separator is configured to remove low gravity solids.
 12. Amethod for separating solids from fluid, the method comprising:obtaining a solid-laden fluid, wherein the solid-laden fluid comprises abase fluid; feeding the solid-laden fluid through a centrifuge; removingat least a portion of high gravity solids from the solid-laden fluids;flowing the solid-laden fluid through a membrane separator; removing atleast a portion of low gravity solids from the solid-laden fluid; andcollecting a permeate from the membrane separator.
 13. The method ofclaim 12, wherein the method further comprises recycling a concentratethrough the membrane separator.
 14. The method of claim 12, wherein themembrane separator comprises a stainless steel membrane separatorsurface sintered with titanium dioxide.
 15. The method of claim 12,wherein the membrane separator comprises a plurality of pores having apore size in a range between 0.02 microns and 0.5 microns.
 16. Themethod of claim 12, wherein the base fluid comprises at least one of anoil-base, a synthetic-base, and a water-base.
 17. The method of claim12, further comprising flowing the solid-laden fluid through a heatexchanger.
 18. The method of claim 12, further comprising adding atleast one of a mud thinner and a demulsifier.
 19. A method of using amembrane separator in an active drilling system, the method comprising:collecting a used drilling fluid; feeding the used drilling fluidthrough a membrane separator; and flowing a permeate into an activedrilling system.
 20. The method of claim 20, wherein the membraneseparator comprises a plurality of pores having a pore size in a rangebetween 0.02 microns and 0.5 microns.